Magnetorheological damper system

ABSTRACT

A magnetorheological damper system comprising a reservoir in communication with a damper. The damper comprises a damper cylinder defining a damper chamber, wherein the damper chamber contains a magnetorheological fluid and a movable damper piston. The damper piston comprises at least two coil windings on the outer surface of the damper piston, wherein the damper piston is capable of generating a magnetic field between the damper piston and a wall of the damper cylinder. The reservoir comprises a reservoir cylinder defining a passageway, wherein the reservoir includes a magnetorheological electromagnet capable of generating a magnetic field between the magnetorheological piston and a wall of the passageway. The combination of the an MR reservoir and MR damper leads to a damping system capable of damping a wide range of extreme forces.

REFERENCE TO GOVERNMENT

[0001] This invention was made with Government support under ContractNos. DAAE07-00-C-L010 and DAAE07-01-C-L018 awarded by the United StatesArmy. The Government has certain rights in this invention.

BACKGROUND OF THE INVENTION

[0002] One of the persistent design constraints in the field ofengineering is vibration and/or force impact and/or fatigue management.That is, nearly all engineered devices and systems must embody a designthat is sufficiently robust so as to safely survive all movement,vibration, impact, etc. that such a device or system is likely toencounter in its useful life. Examples of such areas of engineereddevices and systems are seismic protection devices, constructionhardware, seating systems in vehicles such as helicopters, boats, etc.,manufacturing equipment and the like, all of which relate to the presentinvention as will be self-evident from the text below that describes indetail various preferred embodiments.

[0003] Such design constraints, however, are no more self evident thanin the field of vehicle design. It is well understood that vehiclesendure a constant barrage of forces, impacts and vibrations throughout avehicle's entire useful life. Indeed, when it comes to vehicle design,it may be said that this adverse active environment is perhaps theprimary design constraint.

[0004] The common and long known methodology for meeting these rigorousdesign constraints of vehicle design is the use of a spring and dampersystem located at appropriate locations along the vehicle chassis, mostcommonly between each tire/wheel assembly and the vehicle frame. Themost common type of spring and damper system in this regard is theconventional shock absorber.

[0005] Conventional shock absorbers are comprised of two reciprocatingcylindrical tubes that extend, via an intervening spring, from thetire/wheel of the vehicle to the vehicle frame. One cylindrical tube isfilled with fluid and the other cylindrical tube houses a piston thatpasses through the fluid when the tubes move relative to each other.When the piston moves, it forces the fluid through restrictive passageswithin the piston. This thereby controls the speed with which the twotubes can move relative to each other for a given force.

[0006] When a vehicle encounters a hole or a bump, the tire/wheel movesin response thereto and thereby tends to urge the spring to eitherextend or compress. If there was a spring alone (i.e., no cylindricaltubes discussed above) between the tire/wheel and the frame, there is arisk that this difficult terrain will cause the spring to resonate, acondition that adversely effects the handling and ride of the vehicle.The cylindrical tube structure, therefore, substantially inhibits suchresonating because movement of the spring is dependent on movement ofthe two reciprocating tubes. That is, the added resistance to movementof the tubes due to the restrictive flow of fluid resulting frommovement of the piston thereby dampens the forces that would otherwisecause the spring to extend or compress. This, in turn, substantiallyinhibits spring resonance and ensures proper handling and ride of thevehicle.

[0007] A number of modifications to this basic shock absorber designhave been made over the years in order to enhance the damping effect ofthe device. For example, changing the size of the restrictive passagesin one of the tubes and/or using a fluid with a different viscosity canhave material improved effects on the shock absorber performance.Performance characteristics can also be altered by increasing ordecreasing the size of the shock, changing the design of the tubes, theinternal valving (restrictive passages), etc.

[0008] There are, however, practical limits as to how much shockperformance may be changed by making such alterations. As a result,alternative damping systems have been formulated.

[0009] One such alternative system is based on the utilization of avariable shear strength fluid such as a magnetorheological (MR) fluid.MR fluid based devices are founded on the principle of controlling theshear strength of the MR fluid by inducing and controlling a magneticfield around the piston. Control of this magnetic field can change theshear strength of the MR fluid anywhere from its normal state as aliquid to an energized state that is nearly a solid. Therefore, byprecision control of the magnetic field, the shear strength of the MRfluid is adjusted so as to precisely control the damping performance ofthe device. An example of such an MR device is disclosed in U.S. Pat.No. 6,419,058 which is hereby incorporated by reference in its entirety.

[0010] Nonetheless, the demands placed on vehicles, particularlyoff-road vehicles (as well as other devices and systems that encounter arugged environment), continues to increase, all with the correspondingdemand to avoid any degradation in passenger comfort or endurance. As aresult, there is now an expectation and need to provide a damping systemthat can withstand very sizable range of operating environments, namely,anywhere from a flat, obstruction free surface to the most difficult ofoff-road conditions. Indeed, the system must not only withstand suchenvironments, but must operate effectively and continuously throughoutthis wide range of operating environments without degradation inperformance.

[0011] In this regard, the principle of using MR fluid appears to bewell suited to providing the accurate control necessary for theoperating environment discussed above. However, the inventors are notaware of any prior art MR devices capable of correctly operating at veryhigh damping forces and/or that support wide ranges of damping forceswithout the system either encountering undesired cavitation or withoutbeing severely damaged. Nor are the inventors aware of any prior art MRdevices that have adequate bandwidth for effective isolation of the highfrequency road inputs often encountered with difficult terrains.

OBJECTS AND SUMMARY OF THE INVENTION

[0012] Accordingly, it is an object of the present invention to providea damping device that addresses the known deficiencies in the prior art.

[0013] It is a further object of the present invention to provide adamping device that operates correctly and efficiently at very high andvery low damping forces.

[0014] It is a further object of the present invention to provide adamping device that supports wide ranges of damping forces.

[0015] It is a further object of the present invention to provide adamping device that has adequate bandwidth for effective isolation ofthe high frequency road inputs.

[0016] It is yet a further object of the present invention to provide acontrol system that effectively controls the damping device at very highand very low damping forces.

[0017] It is yet a further object of the present invention to propose anMR device that operates according to the aforesaid objectives.

[0018] It is yet a further object of the present invention to provide anMR device that can be used on vehicles, seismic damping devices andnumerous other devices and systems that demand a damping system.

[0019] It is yet a further object of the present invention to propose anMR device that is relatively straightforward to manufacture andassemble.

[0020] These and other objects not specifically enumerated here arecontemplated by the vibration damping system of the present inventionwhich in one preferred embodiment may include a main housing having amagnetorheological damper valve movable within said main housing and areservoir chamber having a magnetorheological electromagnet and whereinthe main housing and said reservoir are in fluid communication with eachother with a magnetorheological fluid. The system further includes acontrol system which includes a routine for energizing saidmagnetorheological damper valve in response to at least one sensedcondition of said damping system so as to dampen forces exerted on saiddamping system. This routine includes a routine for also energizing saidmagnetorheological electromagnet in response to at least one sensedcondition of said damping system so as to substantially preventcavitation in said damping system over substantially the entireoperating range of said damper system.

[0021] In another exemplary embodiment of the present invention, thereis contemplated a method of damping forces that includes providing amagnetorheological (MR) damping system on a structure that encountersperiodic external forces. The damping system has a movable electromagnetand a stationary electromagnet, both of which being in fluidcommunication with magnetorheological fluid. The system senses at leastone external motion variable on said structure that causes movement ofsaid movable electromagnet. The system then energizes at least saidmovable electromagnet in response to said sensed external force. Thesystem will energize both said movable electromagnet and said stationaryelectromagnet when said sensed external motion variable exceeds apredetermined threshold amount such that cavitation of said dampingsystem is substantially prevented in said damping system beyond saidpredetermined threshold.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The aforesaid object ands and summary are now discussed withreference to specific exemplary embodiments of the present inventionusing the accompanying drawing figures in which:

[0023]FIG. 1 is a perspective view of an exemplary embodiment of themagnetorheological damper system in accordance with the presentinvention;

[0024]FIG. 2 is a cross-sectional view of FIG. 1;

[0025]FIG. 3 is a cross-sectional view of an exemplary embodiment of themagnetorheological damper wherein the damper piston is compressed;

[0026]FIG. 4 is a cross-sectional view of another exemplary embodimentof the magnetorheological damper system in accordance with the presentinvention;

[0027]FIG. 5 is a perspective view of an exemplary embodiment of amagnetorheological damper piston;

[0028]FIG. 6 is a cross-sectional perspective view of FIG. 5;

[0029]FIG. 7 is a cross-sectional side of FIG. 5;

[0030]FIG. 8 is a side view of an another exemplary embodiment of amagnetorheological damper valve in accordance with the presentinvention;

[0031]FIG. 9 is a side view of yet another exemplary embodiment of amagnetorheological damper valve in accordance with the presentinvention;

[0032]FIG. 10 is a side view of one embodiment of a magnetorheologicaldamper valve in accordance with the present invention;

[0033]FIG. 11 is an enlarged cross-sectional view of FIG. 10 taken alongline A-A;

[0034]FIG. 12 is a side view of one embodiment of the internal wiper;

[0035]FIG. 13 is a top view of FIG. 12;

[0036]FIG. 14 is a perspective view of FIG. 12;

[0037]FIG. 15 is block diagram of a control system in accordance withone preferred embodiment of the present invention;

[0038]FIG. 16 is a block diagram of a control system in accordance witha second preferred embodiment of the present invention;

[0039]FIG. 17 is a block diagram of a control system for use incontrolling the damper system set forth in FIG. 2 in accordance with apreferred embodiment of the present invention;

[0040]FIG. 18 is a cross-sectional view of the use of an embodiment ofthe present invention in a vehicle; and

[0041]FIG. 19 is a perspective view of one-half of a mold used topolymer coat the damper valve of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0042] Discussed below is a detailed description of various illustratedembodiments of the present invention. This description is not meant tobe limiting but rather to illustrate the general principles of thepresent invention. It will be appreciated by the reader that theprinciples constituting the invention can be applied with great successto any number of applications that require management of shock forces,vibration, etc.

[0043] With reference to FIG. 1, an MR damper system 100 of the presentinvention is shown and includes a separate reservoir 101 component incommunication with a MR damper 102. However, the reservoir 101 may beintegral with the MR damper 102 as shown in FIG. 4 where the reservoir101 is depicted as being contained within the same structure of the MRdamper 102. As will be discussed in greater detail below, the reservoir101 serves to store and return MR fluid (not shown) that has beendisplaced from the MR damper 102 during compression of the damper 102and is particularly instrumental in achieving the objectives of thepresent invention.

[0044] Again referring to FIG. 1, reservoir 101 comprises a reservoirhousing 103 having two opposite ends which are sealed by a reservoirgland 104 and an end cap (not shown), respectively. The reservoir gland104 and the end cap (not shown) are secured to the reservoir housing 103via threads on the inner diameter of the reservoir housing 103, however,the reservoir gland 104 and the end cap (not shown) can be frictionfitted to the reservoir housing 103, or in certain circumstances, theend cap (not shown) can be integral with the reservoir housing 103 andthe reservoir gland 104 can be coupled to the reservoir housing 103 in afriction-fit or screw-fit relation. It can also be coupled using coldforming of the reservoir housing 103 as well as by other methods knownto one of ordinary skill in the art.

[0045] The reservoir gland 104 includes a through-hole 105 that receivesa conduit 106 which can be steel-braided tubing. The conduit 106 fluidlyconnects the reservoir 101 to the MR damper 102. In an exemplaryembodiment, conduit 106 is capable of handling at least 2000 psi ofpressure, although in other embodiments, the conduit 106 is capable ofhandling at least 3000 psi of pressure. As those skilled in the art willappreciate, different types of tubing having varying pressurecapabilities can also be used to place the reservoir 101 in fluidcommunication with the MR damper 102.

[0046] Continuing with reference to FIG. 1, the MR damper 102 includes adamper housing 107 and a telescoping damper rod 108. At the ends of thedamper housing 107 and the damper rod 108 are a cylinder end 109 and arod end 110, respectively. The cylinder end 109 and the rod end 110 haveopenings 111, 112 that provide attachment points for the MR damper 102to a vehicle's chassis/body and suspension, respectively. As shown inFIG. 1, a bump stop 113, a bump stop cup 114, and rod end 110 areprovided at a second end of the damper rod 108. The bump stop 113 andthe bump stop cup 114 prevent damage to the damper housing 107 in theevent that an especially harsh force causes damper rod 108 to becomefully compressed.

[0047] The damper housing 107 of the MR damper 102 is sealed by acylinder end 109 at a first end and a damper gland 115 at a second endof the damper housing 107 to define an internal chamber 219. Thecylinder end 109 and the damper gland 115 may be coupled to the damperhousing 107 by screw-fit or friction-fit. Alternatively, the cylinder109 end is an integral member of the damper housing 107 or can bescrewed onto the damper housing 107. In an exemplary embodiment, threadsare located on both the cylinder end 109 and the damper housing 107 soas to facilitate the assembly and maintenance of the MR damper 102.

[0048] Referring next to FIG. 2, the internal configuration of thereservoir 101 and the MR damper 102 is shown. In particular, thereservoir 101 comprises a reservoir housing 103 that defines an internalchamber 215 for holding a volume of MR fluid, preferably an amount equalto at least the volume of MR fluid that may be displaced by a fullycompressed damper piston 201 of the MR damper 102. An end cap 202 sealsone end of the reservoir housing 103, which may be secured to thereservoir housing 103 by a screw-fit, friction-fit, or may be integralwith the reservoir housing 103, all of which has been discussedpreviously as to other similar components of the system. As shown inFIG. 2, a gasket, or “O” ring 203, which is positioned on the outercircumference of the end cap 202, seals the end cap 202 in the reservoirhousing 103. The end cap 202 is also provided with a valve 204 whichallows for the introduction of an inert gas such as nitrogen into thespace 205 between the end cap 202 and a reservoir piston 206. Thepurpose of introducing such an inert gas is discussed further below.

[0049] With further reference to FIG. 2, the reservoir piston 206 isgenerally cylindrical and is movable within the reservoir housing 103.The reservoir piston 206 separates the inert gas from the MR fluid thatmay enter the reservoir 101 from the MR damper 102. The reservoir piston206 is provided with two gaskets, 207, 208, to create a seal between thereservoir piston 206 and the walls of the reservoir housing 103.

[0050] The second end of the reservoir housing 103 is sealed with areservoir gland 104. The reservoir gland 104 is a generally puck-shapedstructure having a first face and a second face. The reservoir gland 104also includes first through-hole 209 and a second through-hole 105. Thereservoir gland 104 is also provided with a gasket 210 to create a sealbetween the reservoir gland 104 and the reservoir housing 103. The firstthrough-hole 209 is provided to allow the wires (not shown) thatcomprise the coil windings 218 of the reservoir electromagnet 212 toexit the reservoir 101 and is typically doped with a sealing substanceso as to sealingly retain the wire in place.

[0051] The second through-hole 105 allows MR fluid to either enter orexit the reservoir 101. The reservoir gland 104 also includes a recess213 on the first face that is capable of receiving a bolt 214. The bolt214 secures the reservoir electromagnet 212 to the reservoir gland 104.The recess 213 is positioned on the face of the reservoir gland 104 inorder to center the reservoir electromagnet 212 within the internalspace 215 of the reservoir 101, and thus concentrically within thecylindrical reservoir housing 103. That is, the reservoir electromagnet212 is positioned within the reservoir 101 so as to ensure the existenceof a substantially constant spacing between the outer circumference ofthe reservoir electromagnet 212 and the reservoir housing 103.

[0052] The reservoir electromagnet 212 is a generally cylindrical bodyhaving a centered through hole extending the length of the electromagnet212. The reservoir electromagnet 212 also includes a plurality ofannular recesses 216 provided on the outer diameter of the cylindricalbody. Adjacent annular recesses define ribs 217 on the perimeter of thereservoir electromagnet 212. As illustrated in FIG. 2, the ribs 217 haveradiused outer edges. Alternatively, as illustrated in FIG. 9, the ribs217 may be substantially square. In yet another exemplary embodiment, asillustrated in FIG. 8, the ribs 217 of the reservoir electromagnet 212may be tapered.

[0053] A wire (not shown) is coiled about each annular recess 216 toform coil windings 218. Adjacent coil windings 218 are wound in oppositedirections (as indicated by the arrows in FIG. 5) to generate a magneticflux emitted radially between adjacent ribs when a current is passedthrough the wire (not shown). In one exemplary embodiment, the reservoirelectromagnet 212 comprises at least two coil windings 218. In theexemplary embodiments depicted in FIGS. 2-4, the reservoir electromagnet212 includes four coil windings 218. As those skilled in the art willappreciate, the reservoir electromagnet 212 may have any number of coilwindings 218 depending upon the desired magnetic field.

[0054] As shown in FIG. 10, the coil windings 218 are slightly recessedbetween the ribs 217 of the reservoir electromagnet 212. In an alternateembodiment, the circumference of the coil windings 218 and the walls ofthe reservoir electromagnet 212 may be substantially flush. The distancebetween the coil windings 218 and the wall of the reservoir housing 103as well as the distance between the outermost portion of the reservoirelectromagnet 212 and the wall of the reservoir housing 103 should besubstantially equal in order to promote laminar flow of the MR fluidover the reservoir electromagnet 212.

[0055] In one exemplary embodiment, the wire (not shown) that forms thecoil windings 218 is received in a small in-laid slot in each rib 217 soas to allow the wire to travel to the next adjacent recess 216. Thesein-laid slots are then filled with small piston gap plugs 227 to protectthe wire (not shown) spanning between adjacent annular recesses 216.Alternatively, as shown in FIG. 9, the wire (not shown) may be directedinto through-holes 900, 901 through the ribs 217 into each adjacentannular recess 216.

[0056] Turning now to the MR damper 102 itself, again with reference toFIG. 2, the MR damper 102 includes a damper housing 107 that defines aninternal chamber 219. The internal chamber 219 houses a MR fluid and isbound by the cylinder end 109 and a damper gland 115. According to oneexemplary embodiment, the MR fluid is a hydrocarbon-based fluid havingmicron-sized magnetizable particles suspended in the fluid. For example,in one exemplary embodiment, Lord Corporation MRF-122-2ED fluid may beutilized in the MR damper 102. In another exemplary embodiment, LordCorporation MRF 132AD fluid may be utilized in the MR damper 102. Asthose skilled in the art will appreciate, any MR fluid known ordeveloped in the art may be utilized in the MR damper 102 so long as theproperties of the MR fluid are accounted for in the control algorithmfor the MR damper systems 100.

[0057] A damper piston 201 is positioned within the internal chamber 219of the MR damper 102 and includes piston end 220, a MR damper valve 223coupled to a damper rod 108. The damper piston 201 is capable of movingwithin the internal chamber 219 along the longitudinal axis of thedamper housing 107. With reference to FIGS. 5 and 6, the piston end 220is a puck-shaped structure having a centered through-hole 500, and aplurality of openings 221 positioned about the circumference of thepiston end 220.

[0058] The piston end 220 also includes a linear bushing 222 about theouter diameter of the piston end 220. The piston end 220 is sized tocenter the MR damper valve 223 within the bore of the damper housing107. That is, the piston end 220 ensures that the distance between theMR damper valve 223 and the wall of the damper housing 107 issubstantially constant about the circumference of the MR damper valve223. According to one exemplary embodiment, the linear bushing 222 ismade of steel. In another exemplary embodiment, the linear bushing 222is made of Teflon®-impregnated steel. At those skilled in the art willappreciate, the linear bushing 222 may be made from a plurality ofmaterials such as, but not limited to, aluminum, stainless steel, andtitanium.

[0059] The MR damper valve 223 is a generally cylindrical body having aplurality of annular grooves 224 provided on the outer circumference.The annular grooves 224 are spaced apart forming ribs 225 betweenadjacent annular grooves 224. The annular grooves 224 and ribs 225correspond to the recesses 216 and ribs 217 of the reservoirelectromagnet 212. As with the reservoir electromagnet 212; the ribs 225on the MR damper valve 223 have radiused edges as shown in FIGS. 2-4.Alternatively, the ribs 225 may be squared as shown in FIG. 9. In yetanother exemplary embodiment of the MR damper valve 223, the ribs 225may be tapered (see FIG. 8).

[0060] Turning back to FIG. 2, a rebound stop 226 is positioned belowthe base of the MR damper valve 223. The rebound stop 226 preventsdamage to the MR damper valve 223 should the damper rod 108 extend tothe point where the MR damper valve 223 nearly contacts the damper gland115. According to one exemplary embodiment, the MR damper valve 223 ismade of steel. In another exemplary embodiment, the MR damper valve 223is made from heat-treated steel. As those skilled in the art willappreciate, the MR damper valve 223 may be made from any material havingdirect current magnetic properties.

[0061] The annular grooves 224 on the MR damper valve 223 are sized toallow for a wire (not shown) to be wound within each annular recess 224to form a coil winding (not shown) or a electromagnet. The wire and coilwindings are not shown in FIG. 2 for purposes of clarity in thedrawings, but the wire and coil windings 300 are illustrated in FIG. 3.The coil windings (not shown) of each individual annular recess 224 arewound in opposite directions so that the magnetic field generated byeach coil winding (not shown) passes through the fluid gap, into thedamper housing, back into the fluid gap, and into an adjacent magneticpole. Accordingly, as the MR fluid moves through the openings 221 on thepiston end 220 and past the MR damper valve 223, an electrical currentmay be passed through the wire to create a magnetic field. The magneticfield alters the shear strength of the MR fluid passing between the ribs225 and the damper housing 107. As discussed previously with respect tothe reservoir electromagnet 212, gap plugs 227 protect the wire (notshown) as it spans between adjacent annular grooves 224. Alternatively,as shown in FIG. 9, the ribs 225 of the MR damper valve 223 may beprovided with through-holes 900, 901 that allow the wire (not shown) tospan adjacent annular grooves.

[0062] Turning to FIGS. 3, 4, and 11, the coil windings 300 are alsoprotected by a coating 301. The coating 301 can be a polymer or an epoxycoating. As those skilled in the art will appreciate, other polymerscoatings known or developed in the art may be utilized to encapsulatethe coil windings 300. The number of coil windings 300 and the thicknessof the coating 301 are sized to promote laminar flow of the MR fluidalong the outer surface of the MR damper valve 223. That is, the coatedcoil windings 300 are to have substantially the same circumference asthe MR damper valve 223.

[0063] As shown in FIGS. 2-4, a piston bolt 228 secures the piston end220 and the MR damper valve 223 to the damper rod 108. In theembodiments depicted in FIGS. 2-4, the piston bolt 228 is secured to thedamper rod 108 via threads on the outer diameter of the piston bolt 228and threads on the inner diameter of the damper rod 108. In anotherexemplary embodiment, the damper rod 108 may be secured to the pistonbolt 228 by a friction fit. As shown in FIGS. 2-4, the damper rod 108 isa generally cylindrical member having an inner bore. Wires from the coilwindings 300 are threaded through the damper rod 108 and exit the rodend 110 to a power supply (not shown).

[0064] In one embodiment, a thermocouple or a thermistor (not shown) isdisposed on the end of the piston bolt 228 or the piston end 220 so thatthe temperature of the MR fluid actually present in the chamber may bedetermined. Since temperature is one condition that dictates theoperation of the electromagnets in the system since the properties of MRfluid change with temperature, the presence of the temperature sensorwithin the system itself ensures accuracy and precision in the operationof the system.

[0065] The rod end 110 is coupled to the damper rod 108 by a press-fit,screw-fit, or friction-fit relation. As shown in FIGS. 5-7, the rod end110 has a generally circular head 229 integral with a cylindrical body230 having a main bore 231 extending along the longitudinal axis of thecylindrical body 230. A through-hole 502 perpendicular to the main bore231 of the rod end 110 permits the wires (not shown) from the coilwindings 300 to exit the MR damper 102. The circular head 229 of the rodend 110 is provided with an opening 112 that is adapted to couple to therod end 110 to the suspension (not shown) of the vehicle.

[0066] Turning back to FIGS. 2-3, at the other end of the damper housing107, a damper gland 115 seals the damper housing 107. According to anexemplary embodiment depicted in FIG. 2, the damper gland 115 is screwedonto the damper housing 107 and sealed by at least one gasket 233. Thedamper gland 115 is provided with a centered opening 234 for the damperrod 108 to move through. A generally circular recess 235 or counterboreis provided on the internal face of the damper gland 115. Within therecess 235 is placed an internal wiper 236.

[0067] With reference to FIGS. 12 and 13, the internal wiper 236 is agenerally flat annular disc having a centered opening 1200 that is sizedto fit with very tight tolerance on the outer surface of the damper rod108. The opening 1200 of the internal wiper 236 is characterized by abeveled edge 1201 as shown in FIG. 12. As also shown in FIG. 12, theside of the wiper 236 opposite the beveled edge also has a slight taper.As those skilled in the art will appreciate, the internal wiper 236 maybe made from a plurality of materials such as, but not limited to,brass, steel, titanium, aluminum, metallic alloys, and compositematerials.

[0068] As a result of the tight tolerance between the centered opening1200 and the outer surface of the damper rod 108, the internal wiper 236functions to remove or “wipe” MR fluid from the damper rod 108 as thedamper rod 108 moves in a direction away from the damper housing 107. Inother words, as the damper rod 108 moves past the internal wiper 236,the MR fluid that may have adhered to damper rod 108 is wiped away fromthe damper rod 108 and thereby prevented from inducing excessive wear onthe seal due to the momentum and abrasiveness of the MR fluid.

[0069] Turning to another exemplary embodiment, reference is now made toFIG. 4. The embodiment depicted in FIG. 4 is similar to the MR dampersystem 100 that is illustrated in FIG. 2 with the exception that thereservoir 101 and the MR damper 102 are integral in one cylindricalstructure 400. In this regard, the reservoir 101 and the MR damper 102are in communication by a through-hole 401 positioned on the reservoirgland 402. The reservoir 101 comprises a reservoir electromagnet 212secured to the reservoir gland 402 by a bolt 214 and includes areservoir piston 206 that sealingly engages the cylindrical walls bygaskets 207, 208.

[0070] The reservoir piston 206 divides the reservoir 101 into two areas205, 215. In the first area 205 of the reservoir 101, an inert gas suchas, but not limited to, nitrogen, may be introduced therein by a valve403 positioned on the cylinder end 109. The second area 215 of thereservoir 101 is sized to hold a volume of MR fluid that may bedisplaced from the internal chamber 219 of the MR damper 102 as a resultof movement of the piston 201.

[0071] The internal chamber 219 of the MR damper 113 is defined by thecylindrical wall 400, the reservoir damper gland 402, and the MR dampergland 115. Within the internal chamber 219 is a MR fluid and a MR damperpiston 201. The damper piston 201 comprises a piston end 220 coupled toa MR damper valve 223 and a damper rod 108. The MR damper valve 223comprises a plurality of coil windings 300 which can generate a magneticfield when a current is passed through the coil windings 300. When amagnetic field is generated, the shear strength of the MR fluid thatflows over the MR damper valve 223 increases. Consequently, the forcerequired to move the damper piston 201 through the MR fluid alsoincreases.

[0072] As shown in FIG. 3, a rebound stop 226 is positioned below the MRdamper valve 223 to prevent damage to the MR damper valve 223 or thedamper gland 115 in the event that the damper rod 108 is fully extended.An internal wiper 236 is also positioned within the damper gland 115,and the internal wiper 236 functions to remove MR fluid that may“adhere” to the damper rod 108. The damper rod 108 also includes a rodend 110 and may optionally include a bump stop 113 and a bump stop cup114.

MR Damper System Control and Operation

[0073] Turning next to the control and operation of a MR damper systemin accordance with the present invention, reference is made to FIGS. 15and 16 wherein two alternative approaches to system control aredepicted. The first, FIG. 15, is based on a closed loop controlapproach. The second, FIG. 16, is based on an open loop controlapproach. In this regard, the control scheme depicted in these figuresis directed to control of a MR damper valve 223 in a generic sense. Thatis, these figures do not explicitly identify a control scheme forsimultaneous control of a MR damper valve 223 and a reservoirelectromagnet 212 as such structure is described in exemplaryembodiments described above. A system for such simultaneous control ismore affirmatively identified in FIG. 17, which will be discussed ingreater detail below.

[0074] With reference first to FIG. 15, the closed loop control systemoffers a choice of control algorithms 1502, 1503 to the user which areselected by activation of a switch 1504. Switch 1504 can be a mechanicalswitch, adjusted by a vehicle occupant or operator. Alternatively, theswitch can take the form of a subroutine within the control system thatserves to evaluate the operating conditions of the structure beingdampened and then serves to automatically select the most appropriatecontrol algorithm 1502, 1503 for those conditions. The selection of analgorithm shall depend on the desire of the user or on the programmingof a selection subroutine of the control system. For example, onealgorithm may be particularly well suited for a particularly treacherousoff-road terrain. Another algorithm may be better suited for arelatively flat and smooth terrain. Alternatively, one algorithm may bedesigned to ensure the vehicle maintain certain ride characteristics nomatter what the nature of the terrain. In one exemplary embodiment, theuser or software may choose a control algorithm known to those in theart as a “skyhook” algorithm.

[0075] The choice of the algorithm will then dictate to the system thedesired damper force 1508 depending on various inputs used in thealgorithm that are received in the closed loop control 1506. The inputsto the closed control loop include the damper system temperature 1518,i.e., the temperature of the MR fluid, the damper speed 1520, i.e., thespeed with which the damper rod 108 is actuated upon encountering anobstacle or hole, and the actual damper force 1522. The methods by whicheach of these inputs is obtained will be appreciated as being known tothose of ordinary skill in the art. For example, the temperature of theMR fluid can be obtained with a thermocouple.

[0076] Based on the inputs 1518, 1520, 1522 received by the closed loopcontrol 1506 and governed by the selected algorithm, the control 1506generates a damper current command 1510 (so long as the inputs indicatea signal is needed) and delivers it to a high bandwidth transconductanceamplifier 1512 (discussed in greater detail below). The amplifier 1512then amplifies the signal into an electrical current 1513 that isapplied to the electromagnet (the coils) 1514 of the damper system 1516.This causes the shear strength of the MR fluid to change in directproportion to the magnitude of the electrical current 1513 and thusdampens the movement of the MR damper piston 201 with the system 1516 ina manner that is directly responsive to the actual inputs 1518, 1520,1522. Like all closed loop systems, this system automatically andcontinually adjusts the electrical current 1513 applied to the coilsuntil the actual damper force 1522 matches the desired damper force 1508of the algorithm.

[0077] Turning then to FIG. 16, the open loop control system inaccordance with the present invention is now described. In this regard,as with the closed loop system, the user chooses a desired algorithm,1602, 1603 according to activation of an algorithm switch 1604. Theselection of an algorithm is based on the desire of the user asdiscussed above.

[0078] As with the closed loop system, the choice of the algorithm willthen dictate to the damper specific lookup table 1606 the desired damperforce 1608 depending on various inputs used in the algorithm. A deriveddamper current command 1610 for any given set of parameters isidentified from the “Damper-Specific Look Up Table” 1606. This look uptable 1606 contains data that is based on the characteristics of anactual damper system that conforms to the system that is beingcontrolled. In other words, the look up table is created based onperformance data that is obtained from an actual damper system havingthe same design as the damper unit being controlled by the look uptable. This “actual” data serves to generally “characterize” theoperation of any damper system that is similarly (or identically)designed and therefore this data can be used as general control data forall such damper systems.

[0079] In operation, the damper-specific look up table receives avelocity feedback input 1620 and a temperature feedback input 1618(i.e., temperature of the MR fluid) in addition to the desired damperforce as determined by the algorithm. Based on the values of each ofthese inputs, the system will refer to a look up table that contains theappropriate damper current command so that the damper matches thedesired damper force based on the characterized actual damper. In otherwords, this damper current command is the value that was deemed mostappropriate for the same given inputs on a prototypical damper systemthat was used to generate the look up table. The damper current command1610 is then communicated to the high bandwidth transconductanceamplifier 1612 (discussed in greater detail below) which amplifies thesignal into an electrical current 1613. The current 1613 is then appliedto the electromagnet (i.e., the coils) 1614 of the damper system 1616 tothus change the shear strength of the MR fluid for the purposesdiscussed above.

[0080] Some having ordinary skill in the art perhaps may take theposition that the closed loop system discussed with reference to FIG. 15provides slightly more accurate damping control than the open loopsystem discussed with reference to FIG. 16. This may be based on theability of a closed loop system to constantly monitor the force feedbackdata from the damper and to thereby finely adjust the current command tothe MR damper system 100. However, closed loop systems of this typetypically require complex or at least expensive feedback devices (e.g.,load cells, etc.) and more powerful computing devices, i.e. a fastermicroprocessor, that are not otherwise necessary in an open loop system.Thus for the sake of simplicity and cost, there is perhaps at least aneconomic incentive to control the MR damper 102 using an open loopsystem (i.e., use a look up table) as referenced in FIG. 16. It will beappreciated by those of ordinary skill in the art that either type ofsystem is contemplated as being part of the present invention.

[0081] As a final point regarding the control systems of FIGS. 15 and16, it is noted that both systems utilize a high bandwidthtransconductance amplifier 1512, 1612. Given the advantages thisamplifier adds to the control system, a brief discussion regarding itsoperation is useful.

[0082] In this regard, it will be understood that typically a dampercurrent control command is a low level signal (preferably a voltagesignal but it can also be serial digital, parallel digital, fiber opticor other known means of transmitting data) that must be converted andamplified into a current output of sufficient magnitude to drive the MRsystem electromagnet windings 1514, 1614. It will also be appreciatedthat is very desirable in the context of the present invention toexercise high bandwidth control of the MR damper valve 223 and thereservoir electromagnet 212 so as to maximize the dynamic performance ofthe system. However, the windings 218, 300 on each of these componentshave significant electrical inductance by virtue of their need togenerate large damping forces, such large damping forces being achievedby magnetizing the MR fluid in the gaps between the ribs 217, 225 andhousing 103, 107. This high inductance makes generation of a currentoutput of sufficient quality to achieve high bandwidth from a low levelsignal control virtually impossible without a current amplifier of sometype.

[0083] It is to address these competing interests that the highbandwidth transconductance amplifier in accordance with the presentinvention is used. In this regard, the present invention contemplatesthe use of a hysteretic switchmode transconductance amplifier, i.e., atransconductance amplifier that utilizes a hysteretic switchingtechnique as opposed to fixed frequency switching. Such a hystereticswitching technique ties the switching frequency and duty cycle of theamplifier to the proportion of error between the desired and measuredcurrent through the coil windings 218, 300 as opposed to a set fixedfrequency. In addition, this type of amplifier incorporates a DC/DCconverter that increases the voltage that can be supplied to the damperfrom, say 12 VDC to 60 VDC to further improve transient response of thesystem. However, operation of the high bandwidth transconductanceamplifier is still possible without such a supplemental DC/DC converter.

[0084] Through the use of a high voltage input and the hystereticswitching technique, the problems otherwise encountered due to the highinductance windings to inhibit high bandwidth control are substantiallyreduced or even eliminated. For example, the use of a high voltage inputgives the amplifier greater capability to generate larger magnitudes ofcurrent flowing through the coils 218, 300, and to do so at an increasedspeed, over amplifiers using a low voltage input.

[0085] The amplifier, known by those familiar with the art as ahysteretic current mode converter, oscillates at a variable frequencybetween conduction and regeneration. It is the ratio of time spent inconduction to regeneration that defines how much current flows throughthe coil windings. If more coil current is desired by the controlsystem, the amplifier output stage spends a greater proportion of itstime in the conduction phase. If less coil current is desired by thecontrol system, the amplifier output stage spends a greater proportionof its time in the regeneration phase. Because of the large inherentinductance in the coil winding, the amplifier behaves as a synchronousflyback converter, generating voltage potentials greater than the supplyvoltage. In this case, energy stored in the coil winding inductor may beincreased in voltage by the amplifier, and returned to the amplifierpower supply, presumably to be used to re-energize the coil winding at alater time.

[0086] This allows any energy stored in the winding to be recoveredrather than dissipated and facilitates very fast reductions in coilcurrent. Finally, the hysteretic switching technique can approach zero(i.e., it can momentarily apply direct current to the coil winding) whenthe error between the desired and actual current is large. As a result,heat generation within the semiconductor switches is minimized when thecurrents involved are large. Each of these advantages is extremelyconducive to the amplifier achieving the high system bandwidth that isdesired.

[0087] As a last statement regarding the amplifier, it is noted that ina preferred embodiment, the hysteretic switchmode transconductanceamplifier is implemented using an electrical circuit designed with acommercially available HIP4080A integrated circuit from Intersil. Ofcourse, other electronic designs that support hysteretic control arealso known to those of skill in the art.

[0088] As a final discussion regarding a control system in accordancewith the present invention, reference is next made to FIG. 17 whichgraphically depicts a system for controlling the damper system 100 ofFIG. 2. In this regard, a dedicated hysteretic transconductanceamplifier 1708, 1710 is provided for the MR damper 102 and the MRreservoir 101. It is also seen that the MR damper 102 includes sensorsproviding MR fluid temperature feedback 1704 and velocity feedback 1706,i.e., feedback on the velocity of the suspension system as it encountersan obstacle.

[0089] Within the controller (not shown), there is stored the controlalgorithm 1602 (or choice of algorithms as discussed above) along withtwo sets of lookup tables, namely a damper set of lookup tables 1702 anda reservoir set of lookup tables 1700. Each lookup table containscurrent command data that is organized according to both velocity valuesfor the suspension system and desired forces for each velocity value. Inother words, for each value of velocity and for each value of a desiredforce, there is a value corresponding to current demand.

[0090] The control algorithm 1602 determines the value of the desiredforce for a measured velocity which thereby leads to the controllerissuing the necessary current command. In the case of the damper set oflookup tables 1702, the controller issues a damper current command 1712and in the case of the reservoir set of lookup tables 1700, thecontroller issues a reservoir current command 1714. It should be notedin this regard, however, that the only time a reservoir current command1714 is issued is when the velocity is a positive value, i.e., when thedamper rod 108 is being pushed into the damper housing 107. There is noreservoir current command value when the velocity value is negative,that is, when the damper rod 108 is extending away from the damperhousing 107. The reasons for this will become more apparent in thedescription of the operation of the damper system 100 set forth below.Furthermore in this regard, although a preferred embodiment describedherein contemplates a damping system that uses a reservoir valve, theprinciples of the control system described herein are equally applicableto a damping system that does not use a reservoir valve. In such aninstance, for example, there would be lookup tables for the dampingsystem alone.

[0091] In operation, the controller monitors the velocity of thesuspension system and the temperature of the MR fluid within the dampersystem. The measured temperature will dictate which of the damper set oflookup tables 1702 and which of the reservoir lookup tables 1700 toutilize. The selected algorithm will then identify the desired damperforce, which is then translated by the look up table to an appropriatecurrent command 1712 and the appropriate reservoir current command 1714(assuming the velocity value is positive) from the lookup tables 1700,1702, and will then send each of these respective signals to theamplifier 1708, 1710 dedicated to the MR damper 102 and the MR reservoir101, respectively. Each amplifier 1708, 1710 will then convert thesignals to current and energize the windings (coils) 300, 218 of itsrespective electromagnet 223, 212. The energization of these coils 300,218 will then lead to the enhanced damping effect of the MR dampingsystem 100 of the present invention for the encountered force.

[0092] In view of the foregoing, it is now useful to provide an exampleof the actual operation of a damping system 100 in accordance with thepresent invention. Although this description is directed towards adamper 102 used on a vehicle 1800, it will be readily apparent to thosein the art that the present invention has a wide variety ofapplications. In this regard, reference is made to FIG. 2 and FIG. 18where the structure of FIG. 2 is shown mounted on an actual vehicle1800.

[0093] In this example, it is assumed that the control algorithm is onethat mimics a traditional passive damper, i.e., it mimics a device wherethe damping force is proportional to the differential speed between thedamper rod 108 and the damper housing 107. Of course, there arealgorithms that offer far more sophisticated control than the systemjust described, however, for the purposes of this example a simplealgorithm shall suffice.

[0094] Referring to FIG. 18, a vehicle 1800 is shown having mountedthereon the MR damper 102 and reservoir 101. Surrounding the MR damperis a spring 1804 to provide a spring/damper pair that serves tointroduce compliance between the vehicle chassis 1808 and the wheel/tire1810. There are also sensors mounted on the vehicle, namely, anaccelerometer 1814 for measuring wheel/tire acceleration, accelerometer1816 for measuring the sprung mass acceleration, and position sensor1812 for measuring suspension position. Finally, the vehicle 1800 alsosupports a microprocessor-based software controller 1818 and thepreviously described hysteretic transconductance amplifier 1820 alongwith its DC/DC low to high voltage converter 1822. It will be understoodthat the sensors and the amplifier and other electronics are allconnected to the microprocessor.

[0095] At all times the controller 1818 monitors the sensors. In thisexample, the controller 1818 computes the velocity of the suspension bydifferentiating the signal received from the position sensor 1812 andbases its damper force signal thereon.

[0096] As the wheel/tire 1810 of the vehicle 1800 encounters an obstacle1802, the wheel/tire 1810 is forced to move upwardly thereby causing thespring/damper pair to compress rapidly. The controller 1818differentiates the signal from the position sensor 1812 to arrive at asuspension velocity. The control algorithm then reacts to the suspensionvelocity signal by referring to the lookup table (See FIG. 17) for boththe MR damper 102 and the MR reservoir 101 and selecting the dampercurrent command 1713 and reservoir current command 1714 that correspondsto the MR fluid temperature and the desired reactive force for thatvelocity signal under that algorithm. The amplifier 1820 draws powerfrom the DC/DC converter 1822 and quickly energizes the coils 300 of theMR damper valve 223 and the coils 218 of the reservoir electromagnet 212to the current level dictated by the corresponding damper currentcommand 1713 and reservoir current command 1714, respectively.

[0097] From a mechanical point of view, the damper rod 108 is at thistime being driven upwardly into the damper housing 107 and is therebycausing MR fluid to flow over the MR damper valve 223. This flow of MRfluid causes a differential pressure across the damper valve 223 whichitself opposes the upward movement of the damper rod 108. However,additional resistance is introduced due to the increased shear strengthof the MR fluid resulting from the magnetic flux now found in the coils300.

[0098] In the event the controller commands that more current besupplied to the coils 300 of the MR damper valve 223, the magnetic fieldbetween the MR damper valve 223 and the wall of the damper housing 107increases. This increase of course in turn increases the shear strengthof the MR fluid which manifests itself as yet greater increased dampingforce opposing the direction of travel of the damper rod 108.

[0099] However, further explanation is still required to illuminate thefunction and utility of exciting the coils 218 in the reservoirelectromagnet 212. In this regard, it is useful to discuss the flow offluid between the MR damper 102 and the reservoir 101 and the fluiddynamics that can arise in certain circumstances.

[0100] As the damper rod 108 moves into the damper housing 107, thevolume in the damper housing 107 available for holding the MR fluid isdecreased exactly by the volume that the damper rod 108 displaces in thedamper housing 107. Since MR fluid is essentially incompressible, it isforced to travel from the damper housing 107 to the reservoir 101through the conduit 106. Once in the reservoir 101, the MR fluid flowsover the reservoir electromagnet 212 into the internal space 215 of thereservoir 101. As flow continues and pressure builds within thereservoir, the reservoir piston 206 will be displaced by a volume equalto the volume of the damper rod 108 that enters the damper housing 107.The gas, e.g., nitrogen, present in the space 19 behind the reservoirpiston 206 then, of course, compresses and serves to enhance thedampening effect of the system.

[0101] In instances where the velocity of the damper rod 108 into thedamper housing 107 are especially dramatic and thus result in largecontroller demands on the coil 300 of the MR damper 102, there is a needto prevent the risk of cavitation, i.e., the creation of a low pressurevapor bubble, of the MR fluid in the low pressure side of the MR dampervalve 223 (referred to previously). That is, in order to create thedamping forces necessary to counteract a dramatic velocity change in thesuspension, high current must be passed through the coils 300 of the MRdamper valve 223. This high current obviously dramatically increases theshear strength of the MR fluid. As a result, a corresponding dramaticincrease in the pressure differential across the MR damper valve 223 iscreated. This leads to a very high pressure being present on the side ofthe MR damper valve 223 furthest from the damper rod 108 and potentiallya very low pressure being present on the side of the MR damper valve 223nearest the damper rod 108.

[0102] When this low pressure on the side of the MR damper valve 223nearest the damper rod 108 approaches the vapor pressure of the MRfluid, there is the possibility that a vapor bubble is created. Whensuch a bubble is created, the damping system no longer can generatedamping forces from the effect of differential pressure and instead ofthe reservoir receiving only that volume of fluid corresponding to thedisplaced volume of the damping rod 108, the entire volume of fluidswept by the MR damper valve 223 is urged into the reservoir 101.Clearly this is an unacceptable condition and it is primarily for thisreason that the present invention contemplates the energization of coils218 in the reservoir electromagnet 212.

[0103] It is known in the art that creating an increase in the pressurein the space 205 containing the compressible fluid, e.g., nitrogen, ofthe reservoir 101, serves to create an increased “precharge” pressurewithin the entire damping system 100, including in the space behind theMR damper valve 223 nearest the damper rod 108. With the existence of anincreased pre-charge pressure in this area, the damping system 100 isable to endure greater differential pressure between opposing sides ofthe MR damper valve 223 without cavitation. However, increasing thepre-charge pressure in this manner also increases the parasitic springrate of the system and generally limits the effectiveness and quality ofthe damping system.

[0104] Accordingly, the present invention utilizes the reservoirelectromagnet 212 to increase the so called “pre-charge” pressure in thesystem but only in response to the detection of certain large damperforce values that may otherwise induce cavitation. In all otherrespects, the pre-charge pressure will remain as determined by thepressure in the space 205 of the reservoir 101. In other words, whenlarge damper force values are encountered, the control system energizesboth the coils 300, 218 of the MR damper valve 223 and the reservoirelectromagnet 212 (in the manner described with reference to FIG. 17),the former to create the differential forces necessary to respond to thevelocity signal, the latter to increase the “pre-charge” of the dampersystem 100 and thereby prevent cavitation. In this fashion, the presentinvention has the capability to effectively and qualitatively dampenboth “normal” and dramatic forces while also avoiding undesirableparasitic spring forces.

Fabrication

[0105] According to the teachings of the present invention, the MRdamper valve 223 and the reservoir electromagnet 212 may be fabricatedby various methods. Generally, the reservoir electromagnet 212 and theMR damper valve 223 are fabricated by similar methods but thedescription to these various fabrication methods will be directed to theMR damper valve 223. The MR damper valve 223 may be manufactured fromsteel or other magnetizable metals. Annular grooves 224 are thenmachined along the outer diameter of the MR damper valve 223. Accordingto one exemplary method, the annular grooves 224 are tapered as shown inFIG. 8. According to one exemplary method, the edges of the annulargrooves 224 may be radiused as shown in FIGS. 2-7. A lengthwise slot 501traversing through the annular grooves 224 may then be machined into theMR damper valve 223 as shown in FIG. 5. After the MR damper valve 223has been machined, the slot 501 can be deburred to prevent damage to thecoil windings 300. According to one exemplary method, the MR dampervalve 223 may be heat treated to soften the material and improve themagnetic properties of the MR damper valve 223.

[0106] According to one exemplary heat treating method of the presentinvention, the MR damper valve 223 is heat charged in a wet hydrogenatmosphere with a dew point of approximately 75° F. (24° C.) to atemperature of no more than 1740° F. (950° C.) for approximately two toapproximately four hours. In another exemplary heat treating method ofthe present invention, the MR damper valve 223 may be heat charged in ain a wet hydrogen atmosphere with a dew point of approximately 75° F.(24° C.) to 1562° F. (850° C.). The MR damper valve 223 is then cooledat a rate of 180/306° F. (100/170° C.) per hour to 1000° F. (540° C.).Thereafter, the MR damper valve 223 may be cooled at any rate. In otherexemplary methods, different atmospheres such as, but not limited to,pack anneal, vacuum, dry hydrogen, argon, forming gas (comprisinghydrogen and nitrogen) may be used with a treating temperature in the1350/2150° F. (730/1180° C.) range.

[0107] According to one exemplary method of the present invention, theMR damper valve 223 is placed in a jig fabricated for winding the coils300. A length of wire 1000 is then wound around each annular groove 224as shown in FIGS. 10-11. In one exemplary method, the wire 1000 istightly wound approximately 40 to approximately 60 times in each annulargroove 224. As those skilled in the art will appreciate, the number ofwindings may vary depending upon the desired magnetic field.Additionally, the coil windings 300 in each adjacent annular groove 224is wound in alternate directions. For example, if a first coil winding300 is wound in a clockwise direction, the adjacent coil winding 300 iswound in a counter-clockwise direction. In an alternate method of thepresent invention, the coil windings 300 may be wound in the samedirection.

[0108] In yet another exemplary method, thin strips of fiberglassmatting (not shown) may be used to wrap coil winding 300 in each annulargroove 224 each coil segment. In another exemplary embodiment, gap plugs227 may be inserted and secured within the lengthwise 501 between eachcoil winding 300 prior to casting the coil windings 300 in a protectivecoating 301. In order to maintain flexibility of the wires 1000 thatexit the MR damper valve 223, silicon rubber (not shown) may be used toseal the cavities surrounding the wires. The end faces of the MR dampervalve 223, the inner bore of the damper valve 223, and the ends of thewires 1000 can be waxed with mold release to prevent the coating 301from adhering to these parts during the casting process.

[0109] The MR damper valve 223 is then sealed within a mold 1900 (onehalf of the mold 1900 is shown in FIG. 19). The edges of the mold 1900and the mold breaking holes 1901 are sealed with high temperature tape(not shown). Prior to the introduction of the epoxy into the mold, thedamper valve-mold assembly may be heated to approximately 140° F. forapproximately 2 hours. A vacuum is applied to the damper valve-moldassembly and the epoxy to remove as much air from the epoxy and thedamper valve 223. The epoxy is then drawn through mold 1900 and a vacuummay then applied to further remove any air from the epoxy. The epoxy isthen allowed to pre-cure for approximately 12 hours. Thereafter, thedamper valve-mold assembly is heat cycled for approximately 26 hours andallowed to cool. The damper valve 223 is then removed from the mold 1900and any unwanted epoxy that has adhered to the surfaces of the dampervalve 223 can be removed. The completed damper valve 223 may be thencoupled to a piston end 220 and a damper rod 108. Alternatively, thecompleted damper valve 223 may be coupled to a reservoir gland 104.

[0110] According to another exemplary method of the present invention,the polymer coating 301 can be applied to the coil windings 300 by a dipcoating process. The preparation of the damper valve 223 is similar tothe casting method with the exception to the process of coating the coilwindings 300. After the damper valve 223 has been assembled, hightemperature “flash breaker” tape (not shown) is applied over the coilwindings 300 to protect the coil windings 300 during the maskingprocess. According to one exemplary method, the flash breaker tapeshould be able to withstand at least 350° F.

[0111] After the coil windings 300 are taped, masking material is heatedinto a liquid state. According to one exemplary embodiment, McMasterCarr Supply masking material #7762T76 is used. As those skilled in theart will appreciate, any masking material known or developed in the artmay be used in the dip coating process. According to one exemplarymethod, a portion of the damper valve 223 is dipped within the heatedmasking materials. In another exemplary method, the ends of the dampervalve 223 are dipped within the heated masking materials. In yet anotherexemplary method, the whole damper valve 223 is dipped within the heatedmasking materials. In another exemplary method, the masked damper valve223 may be subsequently heated to enhance the bonding between the dampervalve 223 and the masking material.

[0112] Once the masking material has been applied to the damper valve223, the “flash breaker” tape (not shown) is removed from the coilwindings 300. The damper valve 223 is then hung within a dipping chamber(not shown). The dipping chamber is then sealed and vacuumed to removeas much air from dipping chamber. The vacuum is run until air bubblescease to break out of the epoxy. Once the air has been removed from thechamber, the damper valve 223 is submerged within the epoxy forapproximately one hour. The vacuum is then slowly reduced, and thedamper valve 223 is removed from the epoxy when the epoxy begins tothicken. The epoxy on the damper valve 223 is allowed to pre-cure forapproximately 12 hours at room temperature. The damper valve 223 thenundergoes heat cycling to cure the epoxy and remove the maskingmaterial. Optionally, any unwanted epoxy may be cleaned from the dampervalve 223. Once cleaned, the complete damper valve 223 may be coupled toa piston end 220 and a damper rod 108. Alternatively, the completeddamper valve 223 may be coupled to a reservoir gland 104.

[0113] In closing, it is to be understood that the exemplary embodimentsof the present invention disclosed herein are illustrative of theprinciples of the present invention. Other modifications that may beemployed are within the scope of the invention. Thus, by way of example,but not of limitation, alternative configurations of the presentinvention may be utilized in accordance with the teachings herein.Accordingly, the drawings and description are illustrative and notintended to be a limitation thereof.

What is claimed is:
 1. A vibration damping system comprising: a mainhousing having a magnetorheological damper valve movable within saidmain housing; a reservoir chamber having a magnetorheologicalelectromagnet said main housing and said reservoir being in fluidcommunication with each other with a magnetorheological fluid; a controlsystem; said control system including a routine for energizing saidmagnetorheological damper valve in response to at least one sensedcondition of said damping system so as to dampen forces exerted on saiddamping system; said routine including a routine for also energizingsaid magnetorheological electromagnet in response to at least one sensedcondition of said damping system so as to substantially preventcavitation in said damping system over substantially the entireoperating range of said damper system.
 2. A damper system according toclaim 1, wherein said control system is an open loop system.
 3. A dampersystem according to claim 1, wherein said control system is a closedloop system.
 4. A damper system according to claim 1, wherein said mainhousing and said reservoir chamber are integral.
 5. A damper systemaccording to claim 1, wherein said control system provides electricalcurrent to said windings using a high bandwidth transconductanceamplifier.
 6. A damper system according to claim 1, wherein said atleast one sensed condition includes velocity of said damper valve andtemperature of said magnetorheological damper system.
 7. A damper systemaccording to claim 1, wherein said reservoir chamber includes apressurized subchamber for exerting an internal precharge pressure insaid damper system.
 8. A damper system according to claim 7, whereinsaid pressurized subchamber contains an inert gas.
 9. A damper systemaccording to claim 1, further including a wiper disposed on saidmagnetorheological damper valve, said wiper being sized and shaped tosubstantially prevent said magnetorheological fluid from degrading sealsin said system.
 10. A magnetorheological vibration damping system,comprising: a reservoir defining a reservoir chamber, wherein areservoir electromagnet is positioned within the reservoir chamber; saidreservoir in fluid communication with a damper, said damper having adamper chamber; said damper chamber containing a magnetorheologicalfluid and a damper piston movable within the damper chamber, wherein thedamper piston includes a damper electromagnet; one or more sensors fordetecting the temperature of the magnetorheological fluid and fordetecting the velocity of the damper piston; and a control module,wherein the control module is in communication with said one or moresensors; a reservoir amplifier and a damper amplifier in communicationwith the control module, and wherein the reservoir amplifier is incommunication with the reservoir electromagnet, and the damper amplifieris in communication with the damper electromagnet. said control modulecontaining a routine for selectively energizing said reservoirelectromganet and said damper electromagnet so as to ensure desireddamping of external forces over a wide range of operating conditions.11. The magnetorheological vibration damping system of claim 10, whereinthe reservoir electromagnet and the damper electromagnetic comprises oneor more coil windings, wherein adjacent coil windings are wound inalternate directions.
 12. The magnetorheological vibration dampingsystem of claim 10, wherein the reservoir amplifier and the damperamplifier are hysteretic transconductance amplifiers.
 13. Themagnetorheological vibration damping system of claim 10, wherein thecontrol module comprises at least one control algorithm, a damper lookuptable, and a reservoir lookup table.
 14. The magnetorheologicalvibration damping system of claim 13 wherein the at least one controlalgorithm is selected from the group consisting of an off-road terrainalgorithm, a smooth terrain algorithm, and a skyhook algorithm.
 15. Themagnetorheological vibration damping system of claim 10, wherein saidsystem is disposed in a vehicle.
 16. The magnetorheological vibrationdamping system of claim 10, wherein said system is disposed in a seat.17. The magnetoheological vibration damping system of claim 10, whereinsaid system is disposed in a building for damping seismic loads.
 18. Amethod of damping forces comprising: providing a magnetorheological (MR)damping system on a structure encountering periodic external forces,said damping system having a movable electromagnet and a stationaryelectromagnet, both of which being in fluid communication withmagnetorheological fluid; sensing at least one external motion variableon said structure that cause movement of said movable electromagnet;energizing at least said movable electromagnet in response to saidsensed external motion variable; energizing both said movableelectromagnet and said stationary electromagnet when said sensedexternal motion variable exceeds a predetermined threshold amount suchthat cavitation of said damping system is substantially prevented insaid damping system beyond said predetermined threshold.
 19. The methodof claim 18, wherein said magnetorheological damping system is providedon a vehicle.
 20. The method of claim 18, wherein saidmagnetorheological damping system is provided on a building.
 21. Themethod of claim 18, further including sensing the temperature of saidmagnetorheological fluid prior to energizing one of said movableelectromagnet and said stationary electromagnet.
 22. The method of claim21, wherein energizing of said movable electromagnet and said stationarymagnet is also based on sensing the temperature of saidmagnetorheological fluid.
 23. The method of claim 18, wherein saidenergizing of said movable electromagnet and said stationary magnet isperformed using a closed loop control system.
 24. The method of claim18, wherein said energizing of said movable electromagnet and saidstationary magnet is performed using an open loop control system.
 25. Avibration damping system comprising: a main housing having amagnetorheological damper valve movable within said main housing; acontrol system; and, said control system including a routine forenergizing said magnetorheological damper valve in response to ameasured temperature of said magnetorheological fluid.
 26. A vibrationdamping system according to claim 25, wherein said system includes atemperature sensor disposed in contact with said magnetorheologicalfluid.
 27. A vibration damping system according to claim 25, furthercomprising a reservoir chamber in fluid communication with said mainhousing, said reservoir chamber having an magnetorheolgicalelectromagnet.
 28. A vibration damping system according to claim 27,wherein said control system further includes a routine for energizingsaid magnetorheological electromagnet in response to said measuredtemperature of said magnetorheological fluid.